1. Field of the Invention
This invention relates to a tonometer, and more particularly to a non-contact type tonometer which measures intraocular pressure from a correlation between a measured flow pressure of a fluid for transfiguring a cornea of a patient's eye to be tested and a physical quantity showing the transfiguration of the cornea.
2. Description of the Related Art
Conventionally, a non-contact type tonometer is known as disclosed in, for example, U.S. Pat. No. 3,585,849. The related art disclosed in that patent includes a fluid pulse discharger for directing a fluid pulse which has a predetermined time-pressure functional relation against a corneal surface are of a patient's eye in order to transfigure the area from convexity, through applanation, to concavity, a light source to direct a light beam at the surface area, and a light detector to detect and indicate quantities of flux reflection of the light as a function of the time during which the corneal surface is transfigured from convexity, through applanation, to concavity. The related art tonometer measures an intraocular pressure of the patient's eye from the correlation between the time-pressure functional relation of the fluid pulse and the time between the directing of the fluid force against the corneal surface and the occurring of the first applanation of the cornea surface or the time between the first and second applanations.
The aforementioned non-contact type tonometer has the disadvantage that an indispensable condition for proper operation is the invariability of the time-pressure functional relation of the fluid pulse in every measurement. Therefore, if the time-pressure functional relation of the fluid pulse is different between measurements, a measurement error of the intraocular pressure will directly occur. Thus, the conventional non-contact type tonometer has the problem that the accuracy of measurement of the intraocular pressure is difficult to improve.